1. Field of the Invention
The present invention relates to an image display device using an organic EL element, and more particularly, to an image display device capable of performing high-quality display at a reduced voltage with improved definition.
2. Description of the Related Art
In recent years, the demand for a flat panel display device instead of a cathode ray tube (CRT) display device which is the mainstream of a conventional display device has been increasing. In particular, a display device using an organic electro luminescence (EL) element such as an organic light emitting diode (OLED) is excellent in power consumption, weight, thinness, moving picture characteristics, and viewing angle. Therefore, a higher-performance display device has been actively developed, with the result that device characteristics are improved.
A method of writing a pixel signal into a pixel in an image display device using the organic EL element is divided into a voltage program method and a current program method. In general, according to the voltage program method, a write speed is faster. A technology using the voltage program method is described in, for example, Digest of Technical Papers, SID98, pp. 11-14.
According to a method of driving an organic EL display device, which is described in Digest of Technical Papers, SID98, pp. 11-14, during a write period, a voltage of a gate electrode of a thin film transistor for driving an organic EL element (hereinafter referred to as driver TFT) in each of pixels of an organic EL display panel is automatically reset to a voltage (Vdd-Vth) lower than a power supply line voltage (Vdd) by a threshold voltage (Vth). Therefore, a variation in driver TFTs is suppressed, and the light emission of high uniformity can be realized.